The invention may also relate to an electrical contactor of a moderate, preferably direct, current switch which may be subjected to a short-circuit fault condition requiring the contacts to not weld. In this welded-contact fault condition, un-metered electricity is supplied. This can lead to a life-threatening electrical shock hazard, if the load connection that is thought to be disconnected is still live at 230 V AC.
The term ‘moderate’ is intended to mean less than or equal to 120 Amps.
Furthermore, it is a requirement that the opening and closing timing of the electrical contacts in such a moderate-current switch should be more precisely controlled to reduce or prevent arcing damage thereby increasing their operational life.
It is known that many electrical contactors are capable of switching nominal current at, for example, 100 Amps, for a large number of switching load cycles. The switch contacts utilize a suitable silver-alloy which aims to prevent tack-welding but not necessarily arcing. The switch arm carrying the movable contact must be configured to be easily actuated for the disconnect function, with minimal self-heating at the nominal currents concerned.
The non-weld UC (Utilisation Category) levels demanded are also very challenging, irrespective of whether the switch is closing into or carrying the short-circuit currents. In most cases, the very high current-density during a short-circuit condition at the single-contact touch-point can easily create tack-welds.
It is also known that, to reduce the heating effects of high current, the single movable arm may be split into two. However, this does not overcome the problem associated with simultaneous driving of the arms or blades to open and close together. This can lead to serious imbalances within the contact set and actuator, resulting in shock, vibration and increased contact bounce.
The present invention seeks to provide solutions to these problems.